Used with humor, as a simple statement, in a conversation when you strongly disagree with the majority. Originally a French term used in psychiatry to describe a mental disorder in which two or more associated persons share the same delusion. In other words, you are saying "The two of you share the same delusion." Translated "madness between two."
Two others state "G. Dub is an excellent public speaker." In your disagreement, you respond with "Folie a deux!"
Most prominently used in Lauren Faust's reincarnation of My Little Pony show, Friendship is Magic, and its fans who call themselves bronies. It is a pony-speak for "ladies and gentlemen", or more appropriately, "boys and girls". It is related to somepony, anypony, everypony, etc.
"Fillies and gentlecolts! As mayor of Ponyville, it is my great pleasure to announce the beginning of the Summer Sun Celebration!"
-Mayor of Ponyville, The Mare in the Moon pilot episode.
Follicly challenged is merely the etymologically correct spelling of follically challenged, which is a euphemistic term for bald men. The use of the word serves to lampoon the perceived overabundance of "politically correct" synonyms for various minority groups, which first emerged and spread in the mid to late '90s.
My father is severely follicly challenged, but he's learned to cope without resorting to a toupee or a combover.